Art of etching.



EMANUEL SPITZER, OF MUNICH, GERMANY.

ART OF ETCHING.

' Specification of Letters Patent.

Patented Sept. 3, 1907.

Application filed October 29,1904. Serial No, 230,620.

To all whom it may concern:

Be it known that I, EMANUEL Srrrznn, a citizen oi Germany, residing atMunich, Bavaria, Germany, have invented certain new andusefulImprovements in the Art of Etching; and I do hereby declare thefollowing to be a full, clear, and exact description of the invention,such as will enable others skilled in the art to which it 'appertains tomake and use the same.

My invention relates to the art of producing etched objects and inparticular to, the manufacture of photomechanical printing plates orsurfaces.

The object of this invention is to produce by a simplifiedphoto-chemical and mechanical method etched tion offers great advantagesfor the etching of reproductions from autotypic reticulated plate(screen) pictures,

from hand drawings, wood cuts, copper plate and gravings and the like,and in particular where it is desired to reproduce niceties ofreticulated plate effects (screens) not obtained heretofore.

The essential feature and the novelty of the present invention consistsin exposing directly to the action of the etching agent, the copy of anoriginal which is pro duccd in-the sensitive coating or layer of theobject to be etched, said original being, for instance, a drawing or anysuitable photographicnegative or d'iapositive or other original capableof being copied. In other words, the copy is introduced into the etchingbath directly, that is to say, in the state of hardness acquired throughthe exposure to the light, without such accompanying or'previous use ofartificial protecting and hardening processes being necessaryas'rolling'in or melting on of asphaltum dust upon the coating orlayer,enameling, or similar means of procedure. In this process greatattention has to be paid in the first place, to the retaining of the.porosity of the 'parts sometimes extraordinarily fine which haveremained unexposed to light between the exposed elementary divisions ofthe copied picture in the'copying layer so that these parts or passagesallow the passage of the etching agent; and secdifferent parts oi'fer indifferent degrees resistance to rial during the etching process, carehas to be taken that those places which are becoming developed are notattacked too niuch or entirely spoiled. This object may be accomplishedin a most simple manner by allowing the deposits of the etching process,the etching slime or sludge, to remain on the'already attacked places,the etching slime protecting the places covered thereby against anyfurther excessive action of the etching agent and thus against spoilingand destruction of the etching.

The process may for instance be carried out as follows: To the wellcleaned plate or other object to be etched, a coating of a substance,sensitive to the action of light, such as chrome albumen, chromegelatin, or the like, is applied. This may for instance be effected byputting the plate, before or after pouring on the solution, upon acentrifugal apparatus, in order 'to produce by rotation and simultaneouswarming, a thoroughly well dried copying coat or layer which is asuniform as possible and free from grain.

In the manufacture of the copying coat or layer, the wrinkling of thesame, similar to that used heretofore in .phototype work, should beavoided by all means, this wrinkling having been tried by severalexperimenters ior photomechanical reproductions with but only slightsuccess, in as much as s'uch'an arificial graining interferes with thepermeability of the pores to acid,-and also with the desired action ofthe acid on the elementary divisions. vDusting and melting asphaltumdust grain on the etching plate, as hitherto used particularly forengravings, should likewise be avoided, as well as the admixture of anysubstances to p the sensitive layer, which would produce a firm clearlydefined grain in the same. Upon such a smooth, and

as nearly as possible uniform ungiained layer, any

original which admits of copying, such as a drawing or any photographicnegative or diapositive (half-tone, reticulated (screen), line drawing,Rontgen rays 01 other kind) is copied. It is useful to determine therequired degree of copying by means of a photometer. If the copy is toofaint, the etching of the plate is easily spoiled or over-etched, in thecase of the copying having been carried on too far, the permeability ofthe pores to acid is'impaired as well as the aforesaid capability of theelementary divisions to become progress- .ively etched. This capabilityto become progressively ceived, so thatthe entire copy will not presenta thorough hardening of uniform strength but a progressive a progressiveresistance to acids varying in degree. To

this progressive resistance varying in degree corresponds aproportionate progressive etching of the material, so that in theetching process here described, ,the

etching itself will proceed as follows :The copy on the object to beetched, obtained according to the directions heretofore pointed out,after being washed and dried if desired, is exposed, without thenecessity of using any additional protecting means, to the action of anetching agent and particularly an etching agent which will have ahardening action on the gelatin or other coating, such as chlorid ofiron or nitric acid with 1 alcohol 0. the like, the etching beingfinished in one or more baths .of different concentrations in accordancewith the richness in half-tones'or with the purposes for which the plateis intended. In the case of copies fronrstrong negatives for instance,four or even five baths may be used. It is well known, that as regardsthe selection of the kind of etching baths and as regards theconcentration and the temperature of the same, a variety of conditionshas to be taken into account and the etching operation itself requires acertain delicate and artistic sentiment besides experience and training.

In as much as in this etching process, the dividing passages which haveremained unexposed to light and which are between the exposed andconsequently hardened elementary divisions, are unprotected against theaction of the etching agent, the latter will penetrate through thesedividing passages first of all, and will attack the material of theobject to be etched at these places. This beginning of the etchingprocess takes place at those parts of said object which were leastexposed to light, because they are fewer and smaller elementarydivisions and wider dividing passages present in these places ascontrasted with the strongly lighted portions, in which, on thecontrary, the elementary divisions are in excess as compared with thedividing passages not exposed to light and not hardened While in thismanner the'etching of the dividing passages which have not been exposedto light proceeds, and while the etching cavities or sockets becomehollowed out and the small cones form, the heads of which constitute theelementary divisions or minute (microscopic) particles of the picture,the already mentioned capability of these elementary divisions to becomeprogressively etched will become apparent after a while incorrespondence with the progressive hardening'of the same which hadtaken place. The small particles or points at the places least exposedto the light, with only a small head of hardened chromate layer areattacked very readily and the parts of the object to be etched justbelow them begin to be etched. This etching action is now taking placein such a manner that at the termination of the etching process thiswearing away is most pronounced in the case of the parts which have beenless exposed to light, while it is least pronounced in the case of theparts, which have been more exposed to light, and by these means theproportionate deepening ofthe elementary divisions or minute(microscopic) particles is produced. This etching action would howeverfinally become excessive in cases in which delicate results are desired,unless the etching product'(slime or sludge) formed simultaneously inthe process, which in such cases should not be removed by brushing outor the like, protected the small heads beginning to be attacked fromfurther' action. This progressive etching action which is thecharacteristic feature of the present invention, may be varied to meetthe various purposes intended and it may even be so delicate that it ishardly perceptible to the naked eye, and yet it is eflicacious for use,especially for printing purposes. In the case of a printing blockrecommendable to avoid washing and then drying the copy after exposureto light, but to introduce it, on'the contrary, directly intothe-etching bath. The washing out of the copy, for the purpose ofremoving the chrome,

and the subsequent drying, causes a coarseness in the division of thepicture; wherever this'coarseness is desired, in the case forinstance ofcoarser reproductions, the washing out anddrying may take place beforethe etching.

Another novel and important auxiliary means for Y assisting in bringingout the niceties of a picture in accordance with the present inventionconsists in subjecting the etching bath with the object to be etchedcontained therein, to a gradual and progressive warming or to a gradualand progressive-cooling. By reason of this gradual change of temperatureof the etching bath, a progressive dilution or thickening respectivelyof the acid is produced. The more liquid the acid is, the more delicateare the pores of the copying layer which it is able to permeate; and thelarger the pores are, the more concentrated and consequently the moreviscous should the acid be, in order to etch to a sufii-,

cient depth. Thus the progressive warming or cooling of the etchingagent serves the same purpose as an infinite number of baths ofcontinuously varying concentration. The gradually progressing warmingis', for instance, effected by introducing a copy which, has beenproduced on the plate to be etched in accordance with the explanationsgiven above, into an etching bath which appears suitable for the firstpermeation,

such as chlorid of iron of about 42 degrees, (or more or warmed bath istaken, the deeper are thefurrows of the etching; hence for printingblocks which are intended for printing inrotary presses, stronger bathswill for instance have to be used at the beginningof the progressivewarming than in the case of printing blocks which have to be used forprinting in ordinary printing presses for more delicate efiects. It isnot possible to fix a degree of concentration which would be suitablefor'all cases, in as much as the selection of the paper, of the printingink and other conditionsare also of great influence in determining thedepth of the etching required.

The gradually progressing warming, is effected by placing the etchingbath or baths employed into a hot or gradually heated sand bath or waterbath or by any other gradually operating warming device, until the imageon the object contained in the etching b'ath appears etched down to thenicest details; the object is then taken out, cleaned and made ready foruse.

A progressive thickening of the acid which is desirable for somepurposes is produced by placing the etching bath of a certainconcentration, of about 40 or 42 degrees Baum for instance, or more orless, with the plate to be etched contained therein, in cold orgradually cooled water which if desired, might be cooled with ice, or byusing any other gradually operating cooling device.

A further novel and important auxiliary means for assisting in bringingout the niceties contained in the original in accordance with thepresent invention, con

sistsin submitting the object to be etched to an etching bath theconcentration of which is gradually lessened by introducing into theetching bath more or less slowly an acid of a lower degree ofconcentration. If, for instance, the object to be etched has undergonepart of the etching process in a bath of 'iron chlorid of say 42 Baum, adilution of iron chlorid of 41, 40, 39 or less degrees Baum is more orless slowly introduced into said bath. This more or less slowprogressive reduction of the dilution of the acid of the etching bathpro duces similar effects, eventually even to a higher degree, as thegradual and progressive warming described above. i

Having thus fully described my invention, what I claim asnew and desire,to secure by Letters Patent of the United States is:

1. The process of etching, which consists in applying directly tothesurface of the body to be etched a sensitized coating, thenphotographically printing an image upon said sensitized coating, andthen exposing directly all portions of the surface of the sensitizedcoating to the action of an etching agent.

2. The process of etching which consists in applying directly to thesurface of the body to be etched a sensitized coating, thenphotographically printing an image upon said sensitized coating, thenexposing directly all portions of the surface to the sensitized coatingto the action of an etching agent, and leaving the deposits formed bythe etching action undisturbed until the completion of the etchingaction. a

3. The process of etching which consists in applying directly to thesurface of the body to be etched a sensitized coating, photographicallyprinting an image upon the.sensitized coating, introducing said body tobe etched into an etching bath and regulating the etching operation bymodifying the temperature of the bath.

4. The process of etching which consists in applying directlyfto thesurface of the body to be etched a sensitized coating, photographicallyprinting an image upon the sensitized coating, introducing said body tobe etched into an etching bath and then into progressively modifying thetemperature of the bath to regulate the etching.

5. The process of etching which consists in applying directly to thesurface of the body to be etched a sensitized coating, photographicallyprinting an image upon the sensitized coating, introducing said body tobe etched into an etching bath and introducing additional etching fluidof a lower degree of concentration duringthe etching'operation, wherebythe etching bath is progressively diluted.

6. The process of etching which consists in applying directly to thesurface of the body to be etched a sensitized coating, drying saidcoating by centrifugal action, photographically printing an image uponthe sensitized coating, and directly exposing all portions of thesurface of said coating to the action of the etching agent.

In testimony whereof I hereunto aflix my signature in the presence oftwo witnesses.

EMANUEL srrrzn'n.

Witnesses PAUL PinLIPI'soN, Unrssns J. Brwa'rsn.

